How to make this texture/effect?
You can create simple Sine Function which can be controllable (frequency, postion, width, amplitude) and position wave at the bottom of your model. 

Take into account position in 3D space (rotation matter). 

You can rotate your object and apply rotation or switch Z for Y in Separate XYZ node.

In this example I've used Color Ramp to control colour for Roughness input.

Bottom nodes are just for bump, so don't pay too much attention to them.